OBJECTIVES: A. To continue the study of the interaction of carcinogenic and mutagenic properties tumor-inducing agents. Specifically, to study the following: (1) The role played by diet and age in susceptibility of rats to chemically induced neoplasm, (2) The clonal origin of chemically induced tumors, (3) Formation of mutagenic compounds by interaction of m-nitrobenzhydrazide with rat liver microsomes. B. To continue the study of the renin-angiotensin system and its relation to hypertension. Specifically, (1) to study the effects of various concentrations of neurologically active materials on the radioimmunoassay of plasma renin activity, (2) continue the study of the physical properties of renin isolated from human brain tissue.